With development of a mobile communications system, a transmission rate and service quality that the system can provide are increasingly high, and user services also impose an increasingly strict requirement on a transmission rate. To ensure rates for common users and provide higher throughput for some users without substantially increasing configured bandwidth, the 3rd Generation Partnership Project (the 3rd Generation Partnership Project, 3GPP) introduces a carrier aggregation (Carrier Aggregation, CA) technology. Carrier aggregation means that user equipment (User Equipment, UE) can perform uplink-downlink communication by using multiple component carriers (Component Carrier, CC) at the same time, so that high-speed data transmission is supported. When a user rate decreases, some component carriers may be released, and only one resident carrier is retained. A released transmission resource may be used by another user.
Carrier aggregation in an LTE system may be roughly classified into intra-base station cell aggregation, inter-base station cell aggregation, and the like according to base station locations on which aggregated carriers are located. The intra-base station cell aggregation means that component carriers used by UE at the same time are controlled by a same base station and is relatively simple. The inter-base station cell aggregation means that component carriers used by UE at the same time are controlled by different base stations. In a current protocol, only the intra-base station cell aggregation is supported.
A cell temporary identifier (Cell Radio Network Temporary Identifier, C-RNTI) is a temporary identifier allocated by a base station to UE, and only connected-mode UE has a C-RNTI. The base station uses the temporary identifier to transmit downlink data to the UE, allocate an uplink resource, and transmit various types of control signaling. When UE establishes a connection to a cell, a corresponding base station allocates a C-RNTI to the UE, and when the UE is handed over to another cell because of mobility or for another reason, a base station of the new cell allocates a new C-RNTI to the UE. That is, a C-RNTI is valid only in a current cell.
After CA is introduced, UE needs to perform data and signaling transmission with a base station by using two or more cells at the same time and by using two C-RNTIs accordingly. However, in the prior art, aggregated cells belong to a same base station, and for simplified implementation of UE, it is ensured that the base station uses a same C-RNTI to perform data transmission with the UE in two cells. Therefore, it is specified that UE uses only one C-RNTI. However, after inter-base station cell aggregation is introduced, a mechanism for allocating a C-RNTI to UE needs to be introduced, so that normal communication between UE and a base station can be ensured.